The proposed study will investigate T cell defined anti-idiotypic antibodies and their corresponding idiotopes. Sendai virus specific murine T cell clones will be generated and characterized. Anti-idiotypic antibodies will be prepared against these T cell clones. Antibodies which recognize a dominant idiotope on Sendai virus specific T cells and influence the antigen recognition of T cell clones (i.e. either by stimulation in absence of antigen or by suppression of antigen triggered responses) will be tested for their in vitro and in vivo functions. These studies should indicate whether anti-idiotypic antibodies have merits as anti-viral vaccines. The use of this type of vaccine would be of great value as monoclonal antibodies can be prepared at low cost in unlimited quantities to any given antigen which evokes a T cell response. This study will concentrate on T cell defined anti-idiotypes as in many viral infections T cells rather than B cells are crucial for the outcome of the disease. To further define T cell idiotopes, the cDNA of T cell clones which by serological means (i.e. anti-idiotypic antibodies) have dominant idiotopes and T cell mutant clones which have lost these idiotopes (with or without loss of antigen recognition) will be prepared. Probes which encode for the T cell receptor (alpha and beta chains) will be sequenced. Comparing sequences of idiotope positive T cell clones with thoses of T cell clones which are idiotope negative will determine which chain (alpha or beta) and which part of this chain (V,D or J) encodes for the idiotope.